impact-echo scanning for grout void detection in post
TRANSCRIPT
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Impact-Echo Scanning for Grout Void Detection in Post-tensioned
Bridge Ducts - Findings from a Research Project and a Case History (presented at ASCE Structures Congress, Long Beach, California, May 2007)
Authors:
Yajai Tinkey, Ph.D., Olson Engineering, Inc., 12401 W. 49th
Ave. Wheat Ridge, CO 80033,
USA, [email protected]
Larry D. Olson, P.E., Olson Engineering, Inc., 12401 W. 49th
Ave. Wheat Ridge, CO 80033,
USA, [email protected]
ABSTRACT
This paper presents the findings from a research project funded by the National Cooperative
Highway Research Program-Innovations Deserving Exploratory Analysis (NCHRP – IDEA)
Program. Experimental results are presented herein from the research studies which involved a
defect sensitivity study of an Impact-Echo (IE) Scanner to detect and image discontinuities in
post-tensioned ducts of a mockup U-shaped bridge girder and a mockup slab. Different sizes of
ducts were included in this study as well as varying sizes of void defects. Detailed sensitivity
study of non-destructive grout defect detection with Impact-Echo Scanning of 8-four inch
diameter ducts with constructed defects was the main focus in this study. Comparisons of the IE
defect interpretation and the actual design conditions of the ducts inside the bridge girder/slab are
presented. The IE results are presented in a three-dimensional fashion using thickness surface
plots to provide improved visualization and interpretation of the internal grout to void defect
conditions inside the ducts of the girder. The Impact-Echo tests were performed with a Scanner
which greatly facilitates the Impact-Echo test process by allowing for rapid, near continuous
testing and true “scanning” capabilities to test concrete structures. The paper summarizes the
general background of the Impact-Echo technique and the Impact-Echo Scanner. Descriptions
of two mock-up specimens used in the experiment and the discussion of the results from the
Impact-Echo Scanner are presented herein. Finally, a case study using an Impact Echo Scanner
to locate grout voids inside the Orwell Bridge in UK is included in this paper.
INTRODUCTION
Post-tensioned systems have been widely used for infrastructure bridge transportation systems
since late 1950s. However if a good quality control plan is not implemented during construction,
there is the potential problem during construction that the duct may not be fully grouted. This
results in voids in some areas or inefficient protection for prestressing steel. Over the long term,
water can enter the tendon ducts in the void areas resulting in corrosion of the tendon. The
collapse of the Brickton Meadows Footbridge in Hampshire (UK) in 1967 is the first serious case
of corrosion of tendons leading to major catastrophe (1). In 1985, the collapse of a precast
segmental, post-tensioned bridge in Wales (Ynys-y-Gwas Bridge) was attributed to corrosion of
the internal prestressing tendons at mortar joints between segments (1 and 2). Corrosion-related
failures of post-tensioning tendons have been found in several major segmental bridges such as
the Niles Channel Bridge near Key West, FL in 1999 and Midway Bridge near Destin, FL in
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2000 (3). In addition to actual failures, corrosion damage was found in many post-tensioned
bridge ducts in bridges still in use in Florida and East Coast areas (4).
In post-tensioned structures, quantifying the incidence of corrosion is further complicated by
limitations in techniques for detecting corrosion. Condition surveys of post-tensioned structures
are often limited to visual inspections for signs of cracking, spalling and rust stain. This limited
technique may overlook corrosion activity. Corrosion damage in post-tensioned elements has
been found in situation where no exterior indications of distress were apparent (4). As a matter
of fact, the Ynys-y-Gwas Bridge in Wales had been inspected 6 months prior to the collapse, and
no apparent signs of distress were observed (2). Examples such as this one lead some to fear
that inspection based on limited exploratory or visual inspections may be unconservative and
may produce a false sense of security. The X-ray method is the oldest technique applied
successfully to detect unfilled ducts. However, the method suffers from many disadvantages.
The first disadvantage is that the X-Ray test needs accesses to both sides of the structure, which
is not usually practical in testing bridge ducts. Second, the inspection areas are relatively small
and the test time relatively large resulting a slow testing process. Finally, the need for sufficient
radiation protection and personnel evacuation is usually a problem. Therefore, it is important to
develop a reliable method to practically inspect the quality of grout fill inside the ducts non-
destructively after the grouting process is complete and for inspection of older bridges.
BACKGROUND OF THE IMPACT ECHO TECHNIQUE
The Impact-Echo test involves dynamically exciting a concrete structure with a small mechanical
impactor and measuring the reflected wave energy with a displacement transducer. The
resonant echoes in the displacement responses are usually not apparent in the time domain, but
are more easily identified in the frequency domain. Consequently, linear amplitude spectra of
the displacement responses are calculated by performing a Fast Fourier Transform (FFT)
analysis to determine the resonant echo peak frequencies in the frequency domain from the
displacement transducer signals in the time domain. The relationship among the echo frequency
peak f, the compression wave velocity VP, and the echo depth D is expressed in the following
equation:
(1) D = βVp/(2*f)
where β is a shape factor which varies based on geometry. The value of β was found by
theoretical modeling to be equal to 0.96 for a slab/wall shape (5).
Impact-Echo Scanner
The Impact-Echo rolling Scanner was first conceived by the second author of this paper and
subsequently researched and developed as a part of a US Bureau of Reclamation prestressed
concrete cylinder pipe integrity research project (6). This technique is based on the Impact-Echo
method (5 and 7). In general, the purpose of the Impact-Echo test is usually to either locate
delaminations, honeycombing or cracks parallel to the surface or to measure the thickness of
concrete structures with typically one-sided access for testing (pavements, floors, retaining walls,
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tunnel linings, buried pipes, etc.). To expedite the Impact-Echo testing process, an Impact-Echo
scanning device has been developed with a rolling transducer assembly incorporating multiple
sensors, attached underneath the test unit. When the test unit is rolled across the testing surface,
an opto-coupler on the central wheel keeps track of the distance. This unit is calibrated to impact
and record data at intervals of nominally 25 mm (1 inch). If the concrete surface is smooth, a
coupling agent between the rolling transducer and test specimen is not required. However, if the
concrete surface is somewhat rough, water can be used as a couplant to attempt to improve
displacement transducer contact conditions. The maximum frequency of excitation of the
impactor in the scanner used in research is 25 kHz. The impactor in scanner can be replaced for
an impactor that generates higher frequency. A comparison of the Impact-Echo Scanner and the
point by point Impact-Echo Scanner unit is shown in Figure 1. Typical scanning time for a line
of 4 m (13 ft), approximately 160 test points, is 60 seconds. In an Impact-Echo scanning line,
the resolution of the scanning is about 25 mm (1 inch) between IE test points. Data analysis and
visualization was achieved using Impact-Echo scanning software developed by the first author
for this research project. Raw data in the frequency domain were first digitally filtered using a
Butterworth filter with a band-pass range of 2 kHz to 20 kHz. Due to some rolling noise
generated by the Impact-Echo Scanner, a band-stop filter was also used to remove undesired
rolling noise frequency energy. Automatic and manual picks of dominant frequency were
performed on each spectrum and an Impact-Echo thickness was calculated based on the selected
dominant frequency. A three-dimensional plot of the condition of the tested specimens was
generated by combining the calculated Impact-Echo thicknesses from each scanning line. The
three-dimensional results can be presented in either color or grayscale.
FIGURE 1 – IMPACT-ECHO SCANNER UNIT AND POINT-BY-POINT IMPACT-ECHO UNIT
GENERAL DESCRIPTION OF THE SPECIMENS AND DEFECTS
The specimen used in this study is a full scale pre-cast girder with eight steel ducts inside.
Construction of the modified Styrofoam defects for the mockup girder is described in this section
as well.
Description of the Mockup Girder and Constructions of Grout Defects
A full scale pre-cast bridge girder (U-shaped) was donated to the research team by EnCon Bridge
Company (Denver, Colorado) for use in grout defect sensitivity studies. The length of the girder
is 30.48 m (100 ft) with a typical wall thickness of 254 mm (10 in). There were four empty
Impact-Echo Scanner
Point-by-point IE-1 Impact-Echo Unit
tube to provide
water for coupling
tube to provide water for coupling
Rolling transducer Displacement transducer
automatic impactors
wheels
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metal ducts (101.6 mm or 4 inches in diameter) inside each wall (Figure 2). The west end of the
girder (6.1 m or 20 ft long) was selected for this study.
FIGURE 2 – U-SHAPED BRIDGE GIRDER WITH EIGHT EMPTY DUCTS - WEST END VIEW
Stepped and tapered Styrofoam rods (101.6 mm or 4 inches in diameter) were inserted into
the ducts before grouting to form internal voids with sizes ranging from small to almost full
diameter voids. Figure 3 shows a Styrofoam rod being inserted into the top duct of the north
wall. A wire (3 mm or 1/8 inch in diameter) was bent to form a leg for the Styrofoam rod so that
the foam would be positioned on the roof of the duct, which simulates the real world grout
defects formed by air and water voids. Smaller defects were glued directly to the roof of the duct
since they were too thin for the wire leg. Figure 3 also shows the front view of a Styrofoam
defect inside a duct. The defect sizes are presented in Table 1 in terms of their circumferential
perimeter and duct depth lost. The defect designs are shown in Figure 4a for all four ducts in the
South web wall and Figure 4b for all four ducts in the North web wall. The actual percentage of
circumferential perimeter and diameter depth lost due to the defect are shown in the underlined
numbers placed directly above the defects in Figures 4a and 4b.
Defect ID
Circumferential
Lost (mm, in)
Depth Lost
(mm, in)
Percentage Lost in
Circumferential
Permineter (%)
Percentage
Lost in Depth
(%)
1 50.8, 2 6.35, 0.25 16 6
2 77.2, 3 13.6, 0.535 24 13
3 101.6, 4 23.4, 0.92 32 23
4 127, 5 34.8, 1.37 40 34
5 159.5, 6.28 50.8, 2 50 50
6 192.3, 7.57 66.8, 2.63 60 66
7 217.7, 8.57 78.2, 3.08 68 77
8 243.1, 9.57 87.9, 3.46 76 87
9 268.5, 10.57 95.2, 3.75 84 94
TABLE 1 – STYROFOAM DEFECT SIZES
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FIGURE 3 – STYROFOAM SUPPORTED BY WIRE ROD (LEFT), THE FOAM ROD BEING INSERTED INTO THE DUCT TO FORM
VOIDS (CENTER) AND VIEW OF STYROFOAM DEFECT INSIDE A DUCT (RIGHT)
FIGURE 4a – DESIGN GROUT DEFECTS (STYROFOAM VOIDS) IN THE SOUTH WALL IN 101.6 MM (4 INCH) METAL
DUCTS FROM TOP DOWN
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FIGURE 4b – DESIGN GROUT DEFECTS (STYROFOAM VOIDS) IN THE NORTH WALL IN 101.6 MM (4 INCH) METAL
DUCTS FROM TOP DOWN.
EXPERIMENTAL IE SCANNER RESULTS FROM THE MOCKUP GIRDER
Interpretation of Impact-Echo Data
Localization of grouting discontinuities through Impact-Echo in the mockup girder was based on an
analysis of variations in the Impact-Echo thickness echo depth/frequency. A direct echo from the void or
duct wall, measured as an Impact-Echo frequency corresponding to the depth of the discontinuity (given
by the formula in equation (1) above) has not yet been observed with the IE Scanner. However, as
previously found by others, the IE results indicate the presence of well-grouted, filled tendon ducts by a
nil to minor increase in apparent wall thickness over a grouted duct (typically on the order of 12.7 mm or
0.5 inches or less but larger in the research due to the 3 day age of the comparatively weak grout versus
the hardened, mature concrete). Grouting defects (Styrofoam voids) inside the ducts cause a more
significant increase of the apparent wall thickness in IE results as presented herein vs. well-grouted
ducts). This is in accordance with the interpretation of the Impact-Echo signal as a resonance effect,
rather than a reflection of a localized acoustical wave, i.e., the void may be simply thought of as a hole in
the web wall that due to decreased section stiffness causes a reduction in the resonant IE echo frequency
and a corresponding increase in thickness.
Discussion of Impact-Echo Results
The Impact-Echo tests were performed using a rolling IE Scanner at 1, 3 and 8 days of grout age after the
duct grouting process was completed by Restruction Corporation of Sedalia, Colorado. This paper
presents results from the South and North walls for testing conducted 3 days after the grouting of the
ducts was completed. Ultrasonic Pulse Velocity tests were performed on a sample of the grout placed on-
site in a 406.4 mm (16 in) long duct section. The grout velocity at 3 days old was 11,400 ft/sec,
indicative of solid grout but about 25 % slower than the velocity of the mature, hardened web wall
24” 60”
96” 132”
168” 204”
240”
32%,2340%,34
50%, 60%,66
68%,7784%,94
27.375” 63.375”
96” 132”
168” 204”
16%,624%,13
32%,2340%,34
50%,5076%,87
240”
22” 58”
96”
204” 240”
16%,6
16%,6
84%,9484%,94
Void
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concrete. The results from the IE scanning of the South wall are presented in a thickness tomogram
fashion as shown in Figures 6 – 8 from the South wall and in a normalized thickness tomogram as shown
in Figures 9 - 11 from the North wall. Figures 6 – 11 all show the experimental results compared with the
actual defect designs of the ducts. The drawing of the actual defect design is placed above the
experimental results of the duct for comparison purposes.
Experimental Results from the South Wall
South Wall – Top Duct: The IE Scanner results from the South Wall with the actual defect design of the
top duct placed above the IE results of the top duct are shown in Figure 5. The results are interpreted to
indicate that the grout defect started to appear at a length of 1.93 m (76 in) and becomes clearly evident at
length of 2.92 m (115 in) from the west end of the duct. The location that the defect starts to appear
corresponds to void with 11% depth lost or 20% circumferential perimeter lost. The location that the
grout defect become more evident corresponds to void with 59% depth lost or 57% circumferential
contact diameter lost. The dominant frequency of the fully grouted duct is approximately 6.4 kHz,
resulting in an apparent Impact-Echo thickness of 28.37 mm (11.17 in.). The dominant frequency shifted
downward to approximately 5.37 kHz for an empty duct, which corresponds to an apparent Impact-Echo
thickness of 340 mm (13.4 in). This is a relatively large thickness shift of over 30% compared to the
nominal thickness of the wall. The interpretation of the Impact-Echo Scanner results, however, shows a
downshift in frequencies from lengths of 5.49 to 6.1 m (216 to 240 in), indicating voids at duct locations
where no discontinuities were intentionally placed. It is likely that grout did not flow into the higher east
duct end due to the big voids in front of it. Radiographic tests will be performed in the future to verify the
design versus actual conditions of the simulated defects.
FIGURE 5 – IE RESULTS FROM THE SOUTH WALL WITH ACTUAL DESIGN DEFECTS OF TOP DUCT
0 60 120 180 240 20 40 80 100 140 160 200 220
Length of Wall (inches)
0
4.8
4
3.2
2.4
1.6
0.8
Wall Height (ft)
72
144180
216
16%, 6%”
84%, 94% 76%, 87%
68%, 77%
Defect appears at length of 76 inches (from West end) – defect size of 20%, 11%
Defect can be identified clearly at length of 115 inches (from West end)
- Defect Size of 57%, 59%
West End East End
8.0
8.75
9.5
10.25
11.0
11.75
12.513.25
14.0
8.0
8.75
9.5
10.25
11.0
11.75
12.513.25
14.0
IES Thickness Echo Scale (inches)
8
South Wall – Second Duct from Top: Review of Figure 6 shows that there are three grout defect
zones. The first grout defect zone correlates with the end defect (13% depth lost or 24%
circumferential lost). The second defect zone shows minor grout problem from lengths of 0.91 –
1.67 m (36 – 66 in) from the west end of the duct. However, there is no actual defect placed in
this area. Radiography is required to confirm the realization of defect designs. The third defect
zone appears at a length of 3.35 m (132 in) which corresponds to defect of 9% in depth lost or
18.5% in circumferential lost. The most apparent grout defect appears at a length of 5.18 m (204
in) corresponding to the location of the largest Styrofoam in the duct (87% depth lost or 76%
circumferential perimeter lost). Similar to the results from the top duct, the interpretation of the
Impact-Echo Scanner results, however, shows a downshift in frequencies from lengths of 5.18 to
6.1 m (204 to 240 in), indicating major voids at duct locations where actual defect shape tapers
down toward the east end. It is likely that grout did not flow into the east end due to the large
voids in front of it.
South Wall – Third Duct from Top: Figure 7 shows three zones of grout defects. The first area
is located at the west end where Styrofoam Defect ID# 3 (see Table 1) is in place. However, the
IE results show that the duct is fully grouted between lengths of 0.45 – 2.13 m (18 – 84 in) from
the west end where there are actual Styrofoam defects placed in these locations. The grout
defect appears again between lengths of 2.13 – 3.2 m (84 – 126 in). The starting location of the
second defect zone corresponds to actual defect of 49% depth lost or 48% circumferential lost.
The end location of the defect zone corresponds to actual defect of 30% depth lost or 34%
circumferential lost. The interpretation of the Impact-Echo Scanner results, however, shows a
downshift in frequencies from lengths of 3.48 – 6.1 m (137 to 240 in), indicating minor to major
voids at duct locations where no actual Styrofoam defect in place. Radiography is required to
confirm the actual location of Styrofoam voids.
FIGURE 6 – IE RESULTS FROM THE SOUTH WALL WITH ACTUAL DESIGN DEFECTS OF SECOND DUCT
240
East End
16%, 6%
0 60 120 180 20 40 80 100 140 160 200 220
Length of Wall (inches)
0
4.8
4
3.2
2.4
1.6
0.8
Wall Height (ft)
West End
36”
240
204
132
24%, 13%
16%, 6%
76%, 87%
Grout defect appears at
length of 135 inches – Defect Size 24%,
13%
Worst defect area
Minor grout defect where
there is no Styrofoam
Grout defect appear at
Lengths of 6 – 30”
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FIGURE 7 – IE RESULTS FROM THE SOUTH WALL WITH ACTUAL DESIGN DEFECTS OF THIRD DUCT
Experimental Results from the North Wall
North Wall – Top Duct: The IE results from the North Wall with the actual defect design of the
top duct placed above the IE results of the top duct are shown in Figure 8. Several pieces of
stepped Styrofoam were inserted inside this duct ranging from depth lost of 23% to 94% or
circumferential lost of 32% to 84%. All the results from four ducts from the North wall are
presented with normalized thickness tomogram. The results are interpreted to indicate that the
grout defect started to appear at the west end of the girder although there was not Styrofoam
inside the duct for the first 6.10 m (24 inches) from the west end. However, visual inspection
indicated there was honeycomb around the top duct of the north wall. Figure 8 showed that the
IE test was able to detect the grout defect of 23% depth lost or 32% circumferential lost. The
location that the grout defect is more evident corresponds to void with 50% depth and 50%
circumferential contact diameter lost.
0 60 120 180 240 20 40 80 100 140 160 200 220
0
4.8
4
3.2
2.4
1.6
0.8
Wall Height (ft)
29”
65”
101”
137”
16%, 6%2”
76%, 87% 16%, 6%
40%, 34% 32%, 23%
Length of Wall (inches) West End East End
Grout defect appears
from lengths of 84 - 126 inches
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FIGURE 8 - IE RESULTS FROM THE NORTH WALL WITH ACTUAL DESIGN DEFECTS OF TOP DUCT AND THE
NORMALIZED THICKNESS SCALE
North Wall – Second Duct from Top: Several pieces of stepped Styrofoam were inserted inside
this duct ranging from depth lost of 6% to 87% or circumferential lost of 16% to 76%. Review
of Figure 9 shows that the grout defect started to appear at a length of 1.62 m (64 in) from the
west end of the girder. This length corresponds with location with voids of 13% lost in depth or
24% circumferential lost.
North Wall - Third Duct from Top: Review of Figure 10 shows that the grout defect started to
appear at a length of 2.59 m (102”) from the west end of the girder. This location corresponds to
void of 11% depth lost or 19% circumferential lost. In this case, the grout defect appear to be
apparent (full depth void) right at a length of 3.35 m (132 in) from the west end. This location
corresponds to void of 35% depth lost or 39% circumferential lost.
2460
96132
168204
240
32%, 23% 40% 34%
50%, 50% 60%, 66%
68%, 77% 84%, 94%
Length of Wall (inches)
48 96 144 240 16 32 64 80 112 128 160 224 0
West End East End
176 192 208
0
4.8
4
3.2
2.4
1.6
0.8
Wall Height (ft)
Grout defects start to appear at the west end
Grout defect becomes clear
11
27.37563.375
96132
168204
16%, 6% 24%, 13%
32%, 23% 40%, 34%
50%, 50% 76%, 87%
240
Length of Wall (inches)
48 96 144 240 16 32 64 80 112 128 160 224 0
West End East End
176 192 208
0
4.8
4
3.2
2.4
1.6
0.8
Wall Height (ft)
Grout defect appears at a length of 64 inches
FIGURE 9 – IE RESULTS FROM THE NORTH WALL WITH THE ACTUAL DESIGN DEFECTS OF THE SECOND DUCT
FIGURE 10 – IE RESULTS FROM THE NORTH WALL WITH THE ACTUAL DESIGN DEFECTS OF THE THIRD DUCT
CASE HISTORY
The results obtained from the research project were applied to a real world application. This
section presents an example case history using the Impact Echo Scanner to locate anomalies
inside post-tensioned bridge ducts inside the Orwell Bridge in UK (Figure 11). The testing was
conducted typically from inside each bridge from one side of each of the web walls with the
Impact Echo (IE) Scanning system. The tests were typically performed in vertical lines located
approximately every 2 meters (m) along a web wall and each vertical scan generally started from
22” 58”
96”
204” 240
16%, 6%
16%, 6%
84%, 94%
Length of Wall (inches)
48 96 144 240 16 32 64 80 112 128 160 224 0
West End East End
176 192 208
0
4.8
4
3.2
2.4
1.6
0.8
Wall Height (ft)
Grout defect appears at 102”
12
the bottom inside chamfer and ran to the top inside chamfer of the tested web walls for about 72
tests over 1.8 m of wall. A 2-D scan vertically up the wall from 0 to 2 m is shown in Figure 12.
The 2-D results shows a single time domain result and the corresponding linear frequency
displacement spectrum showing the resonant thickness echo peak along with the thickness vs.
distance plot that is the 2-D IES result. Potentially voided ducts are indicated by the greater
thicknesses in 2 locations (lower resonant frequency echo peaks due to voiding) in Figure 12.
The results from the tests are presented in a thickness tomogram fashion for each web wall for
each tested span with thicker areas indicative of potential void in the PT Ducts. An example test
result from one of the spans is presented in Figure 13. Review of Figure 13 shows
discontinuities or voids located at 20 m from Pier 2 and from the bottom of the wall (location
where the scan started) to a height of 0.6 m. The IE records indicated cracks/voids at depths of
12 – 15 cm from the test surface. In addition, the plot in Figure 13 also indicated a thicker area
(presented in black color) representing voids inside the duct(s) located at 42 m from Pier 2 and
from heights of 0.9 – 1.15 m. The color map in Figure 13 shows normalized thicknesses (the IE
thickness divided by the nominal thickness at the tested line) by color from 0.1 to 1.3.
FIGURE 11 – ORWELL BRIDGE
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FIGURE 12 – VERTICAL IMPACT ECHO SCAN WITH 2 DUCT VOIDS OF 33 CM THICK WALL SECTION WITH 100 MM
DUCTS
Duct Voids
shown by shift in
thicknesses of 38
to 44 cm vs Wall
Echo of 33 cm
1.8 m at
end of
IE scan
O m at
start of
IE scan
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FIGURE 13 – 3D NORMALIZED THICKNESS TOMOGRAM OF SPAN 2 OF NORTH BOX (GENERAL CONDITION)
SUMMARY
The results from the IE tests using portable rolling IE Scanner system show good agreement with the
actual defect design. In the IE testing by the authors to date, the clearest indication of the presence of
grouting defects is the apparent increase in the thickness due to a reduction in the IE resonant frequency
as a result of the decrease in stiffness associated with a defect. No direct “reflection” from the ducts with
grouting defects was observed in these experiments. This is because of larger wavelength generated by
the impactor inside the Impact-Echo Scanner. In this study, with the help of 3D visualization, the IE
scanning was able to identify voids as small as 9% depth lost or 20% circumferential diameter lost of a
101.6 mm or 4 inch diameter steel duct.
ACKNOWLEDGEMENTS The financial support from the NCHRP-IDEA program of the Transportation Research Board of the
National Academy of Sciences which made this research project possible is greatly appreciated by the
authors. The authors would also like to express their gratitude to Mr. Jim Fabinski of EnCon Bridge
Company (Denver, Colorado) for donating a full scale bridge girder for use of this research and the
assistance of Restruction Corporation in grouting the ducts.
Discontinuity at 20 m. from the ref.
(depth of 12 – 15 cm from the test surface)
0
0.4
0.8
1.2
1.6
22 32 42 52 622 12
2
Voids inside ductsPier 2 Pier 3
Height (meter)
Distance (meter)
Discontinuity at 20 m. from the ref.
(depth of 12 – 15 cm from the test surface)
0
0.4
0.8
1.2
1.6
22 32 42 52 622 12
2
Voids inside ductsPier 2 Pier 3
Height (meter)
Distance (meter)
15
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Society, 1996
[2] Woodward, R.J. and Williams, F.W., “Collapse of the Ynys-y-Gwas Bridge, West Glamorgan,”
Proceeding of The Institution of Civil Engineers, Part 1, Vol. 84, August 1988, pp. 635-669.
[3] Florida Department of Transportation (FDOT) Central Structures Office, “Test and Assessment of NDT Methods
for Post Tensioning Systems in Segmental Balanced Cantilever Concrete Bridges, Report, February 15, 2003.
[4] J. S. West, C. J. Larosche, B. D. Koester, J. E. Breen, and M. E. Kreger, “State-of-the-Art Report about
Durability of Post-tensioned Bridge Substructures”, Research Report 1405-1, Research Project 0-1405, Texas
Department of Transportation, October 1999.
[5] Sansalone, M. J. and Streett, W. B., Impact-Echo Nondestructive Evaluation of Concrete and Masonry. ISBN: 0-
9612610-6-4, Bullbrier Press, Ithaca, N. Y, 1997 339 pp.
[6] D. Sack and L.D. Olson, “Impact Echo Scanning of Concrete Slabs and Pipes”, International Conference on
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[7] ASTM C1383 "Test Method for Measurement P-Wave Speed and the Thickness of Concrete Plates Using the
Impact-Echo Method".